The present invention relates to sealed ingredient container devices and more particularly to hermetically sealed electrochemical container devices including safety vents therein and a method of making safety vents for such devices.
It is well known to provide a rupturable safety vent in a container body which ruptures when gas pressure develops within the container beyond a predetermined limit to permit gas release in a manner to avoid uncontrollable container disassembly or disintegration with possible concomitant damage to surrounding environment and personnel. It has been recognized that past safety vent forming means have resulted in residual stresses, stress corrosion, non-uniformity in metal thickness and deformed metal grain structure leading to non-uniform pressure sensitivity and pressure responsitivity characteristics. It also has been recognized that safety vents which allow small leaks and which limit the rate of escape of undesirable elements do in some instances serve to permit pressure build-up to a level where uncontrollable and undesirably damaging explosions of the container to be vented occur, such as in a lithium battery, where slow venting can allow battery temperature increase to the melting point of lithium, which in the presence of electrolyte can result in violent explosions. In U.S. Pat. No. 4,803,136, issued to Benjamin Bowsky et al on Feb. 7, 1989, several of these problems have been recognized, including the need for a safety vent which provides for profound and instantaneous rupture. This patent calls for an etching process to produce a flat safety vent membrane of uniform thickness and preselected surface area to have a controlled and uniform pressure sensitivity of substantially unchanged residual stress, the membrane being capable of withstanding a selected pressure before profoundly rupturing. In U.S. Pat. No. 4,993,602, issued to Donald P. Casey on Feb. 19, 1991, it is recognized to provide a safety vent opening in a pressurized container with a sealing member positioned over the opening to be normally retained in sealing relation with the opening to prevent venting through the opening. Upon a rise of pressure in the container to a predetermined cracking pressure, an elastomeric device cooperative with the sealing member compresses to allow the sealing member to yield from the opening. Nothing in the structure of this patent contemplates profound and instantaneous rupture of a sealing membrane and, in fact, the teaching of a "cracking pressure" for an opening covering sealing membrane with the concept of "cracking" is contrary to the concept of profound rupture. In U.S. Pat. No. 5,004,656, issued to Kiyoshi Sato et al on Apr. 2, 1991, a welded double sealing member for perfectly sealing a charging opening of a battery vessel is disclosed, such double sealing member being of a permanent nature and not a safety vent. In fact, this patent--like U.S. Pat. No. 4,803,136--teaches an annular thin groove in the bottom wall of the battery vessel to prevent battery explosion; however, the Sato patent does not indicate how such groove is formed or whether it is capable of profound rupture.
The present invention, recognizing the known pressures vessel safety vent structures of the prior art and particularly the desirability of providing a safety vent structure capable of profoundly rupturing upon reaching a selected pressure, provides a unique and novel pressure vessel safety vent structure capable of achieving such a concept in a comparatively economic and straightforward manner. In addition, the present invention provides a novel economical and straightforward method of manufacturing such safety vent structure with a minimum of manufacturing and assembly steps and with a minimum of tooling and parts. Further, the novel structure of the present invention is capable of effectively operating as a safety vent in smaller battery vessels to be readily responsive to venting at much lower pressure levels than a number of safety vent arrangements of the past.
Various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth herein.